He says he has developed a way to turn waste plastic into automobile fuel. He's seeking governments or companies to build incinerating plants, which he says any city with a recycling program can do near existing collection facilities. And in the process, he says, they'd create jobs, cut landfill demands, and make fuel.

Renewable energy is the "emerging technology" in America, said Sarker, a 43-year-old native of Bangladesh who works for a company called Natural State Research, Inc., of Stamford, Conn.

Sarker's big dreams are part of a much bigger story involving entrepreneurs, government and even nature itself.

Leaders in wind, geothermal, solar, biomass and hydropower this week called for the government to come up with long-term renewable energy standards and to renew or strengthen tax breaks to encourage growth.

While there was impressive growth in some sectors of the renewable field in 2009, in part from tax and other incentives in the nearly $800 billion "stimulus" package, other renewable sectors are hurting. Robert Cleaves, president and CEO of the Biomass Power Association, said the expiration of a tax credit for existing biomass plants at the end of 2009 threatens half of his emerging industry.

Cleaves and his colleagues complained that year-to-year changes in tax codes and federal energy incentives make it difficult to form long-term business plans and attract investors. They said Europe and China have advantageous long-term renewable strategies.

"The importance of building a strong renewable energy manufacturing base in the U.S. cannot be overstated," said American Wind Energy Association CEO Denise Bode. "The U.S. has a historic opportunity to fortify the clean energy economy, but is committing unilateral economic disarmament by not giving itself the power to do so."

But her industry also this week was hit a report by an investigative journalism team out of American University that an estimated 80% of the $2 billion in stimulus spent on wind power went to foreign turbine producers. Bode said she invited foreign investment and that even in the recession, her industry had grown to employ 85,000 Americans.

Robert Wallace, director of the BioEnergy Bridge program at Penn State University, said the economic downturn has created a tough two years for venture funding in the industry. His program is designed to get public, private and university researchers and entrepreneurs working together on a sustainable biomass industry. Asked about the state of the industry, he joked, "What day is it? What time of day? Who did I last talk to?"

Finances and government aren't the only challenges. Natural resource supplies and vagaries also can impede, and so can land-use policies.

There have been reports this winter that turbines in Minnesota, one of the top wind-power states, aren't turning in extremely cold weather.

In geothermal, which relies on resources deep inside the earth, earthquakes are a constant threat.

A recent Government Accountability Office study concluded there are many uncertainties about the impact of increased biofuel production on water supplies. Siting of biomass and hydropower plants is a critical national issue, said Linda Church Ciocci, executive director of the National Hydropower Association.

"All renewable technologies have a constant challenge to be as 'green' as the public wants them to be," said Karl Gawell, executive director of the Geothermal Energy Association. "To keep looking for their problems and addressing them effectively."

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